A color image is formed in a color photographic element by generation of an imagewise distribution of the dye as a function of silver halide development. Typically this is formed by reaction between a coupler compound and oxidized silver halide developing agent. However, dye images can also be formed by other means such as the imagewise diffusion of dye or the imagewise destruction of dye. Regardless of the means by which the dye image is formed, it is common practice to remove the silver image formed on development and silver halide remaining in unexposed areas of the element. This is accomplished by a bleaching step in which the silver image is oxidized by a suitable oxidizing agent, commonly referred to as a bleaching agent, followed by dissolving the silver halide in a silver halide solvent, commonly referred to as a fixing agent. Alternatively, the bleaching agent and the fixing agent can be combined in a bleach-fixing solution and the silver removed in one step by the use of such a solution.
A variety of bleach compositions have been employed with silver halide materials. These include those based on, i.a., ferricyanide, dichromate, permanganate, chloride, quinone, as well as aminocarboxylic acid and persulfate oxidizing agents. Typical compositions containing such oxidizing agents for the bleaching of photographic image silver are referred to or described in U.S. Pat. Nos. 3,512,979; 3,615,513; 3,647,469; 3,689,272; 3,706,561; 3,716,362; 3,749,572; 3,772,020; 3,893,858; 4,163,669; 4,292,401; 4,293,639; 4,301,236; 4,322,493; 4,448,878; 4,458,010; 4,481,290; 4,524,129; 4,546,070; and 4,596,764.
Other descriptions of the composition and use of photographic silver bleaches are found on pages 124 and 125 of Neblette's Handbook of PHOTOGRAPHY AND REPROGRAPHY, Materials, Processes and Systems, Seventh Edition, Van Nostrand Reinhold Company; and on pages 447 to 450 of THE THEORY OF THE PHOTOGRAPHIC PROCESS, Fourth Edition, MacMillan Publishing Co., Inc., Hew York, London.
Various substituted thiols have been found to accelerate bleaching either when directly added to the bleaching solution or, if introduced via a prebath, before the bleaching step. See for example U.S. Pat. No. 3,893,858, issued July 8, 1975.
U.S. Pat. No. 4,163,669, issued August 7, 1979, suggests that there would be an advantage to incorporating the bleach accelerator directly in the photographic film but that incorporation of the free thiol would have adverse effects on the photographic properties of the film. The '669 patent suggests incorporating in a photographic element certain bleach accelerators as the salt of a heavy metal ion. Among the bleach accelerators mentioned are the organic thiols of the type described in U.S. Pat. No. 3,893,858.
While the heavy metal salts described in the '669 patent are effective with bleach compositions based on ferric EDTA, they are not as effective with other bleach compositions as would be desired. Furthermore, these compounds do not help in reducing stain attributed to residual sensitizing of dye.
Accordingly it would be desirable to have bleach accelerator precursor compounds which can be incorporated in a photographic film, which will permit the film to be used in a multiplicity of bleach and bleach-fix compositions with good results, and which will help to reduce sensitizing dye stain.
We have found compounds which can be incorporated in photographic elements as novel bleach accelerator precursors. These compounds are effective to accelerate bleaching of a variety of bleaching and bleach-fixing compositions. Moreover, they help to reduce sensitizing dye stain and do not have adverse sensitometric effects on the element.
In one embodiment our invention is a silver halide photographic element comprising a support, a silver halide emulsion layer, and a bleach accelerator precursor wherein the bleach accelerator precursor is a silver salt of an acid-containing non-zwitterionic, organic thiol, the precursor having a solubility of greater than or equal to 1 g/l silver ion in both (a) a color developing solution comprising a pH of 10, a sulfite concentration of 4.25 g/l and a bromide concentration of 1.3 g/l, and (b) a bleach solution comprising a pH of 6 and a bromide concentration of 150 g/l, when held at 23.degree. C. for five minutes.